Having returned today then I can report that there still is a BP as you leave Fort William as well as an Esso on the other side of the road before it (which was very cheap at £1.14 for normal unleaded today). There is also a Jet at Inverinate and then it was just the Gulf and Gleaner PS mentioned at the various locations above.
if it helps, I topped up the tank at the BP and still had over 3/4 left when I got to Portree. I did hit Eco Mode though. As much has been said, the roads are great but currently packed with tourists, campers & caravans at the moment so unable to enjoy unless on a bike.
So Fort William to Portree and back home on 1 tank with an average mpg in the CS of 41.9 on the computer.